Aircraft that utilize jet engines and which fly at high altitudes require protection against formation of ice in the liquid fuel. For commercial and military aircraft this is usually accomplished by providing heating devices and arrangements for maintaining the temperature of the fuel in the fuel feed system above temperatures at which water dispersed in the fuel would freeze. For small jet planes, such as for private and business use, the cost and complexity of heating devices and systems is relatively high and it has been found that adding an anti-icing liquid to the fuel is an acceptable substitute. However, present methods of calculating and adding correct or optimum amounts of the anti-icing fluid to the fuel are time consuming and subject to human error.